A great deal of commerce is currently aided by the use of electromagnetic communication, and electromagnetics are widely used for sensing, as for example in radar systems. Such radar systems may be used for monitoring the flight path of an aircraft from the aircraft itself for weather and object monitoring, monitoring the airspace around an airport for traffic control purposes, distance and acceleration monitoring between automobiles, and for military purposes. Reflector-type antennas have been, and still are, widely used for obtaining the high gain desired for communication with distant locations, and to obtain a narrow radar antenna beam to allow objects to be located with more precision than if a broad antenna beam were used. Reflector-type antennas are subject to some disadvantages, especially when the antenna beam must be scanned rapidly. Since the direction of the antenna beam as generated by a reflector antenna depends upon the physical position of the reflector, the reflector itself must be physically moved in order to scan the antenna beam. For simple area surveillance, this is not a problem, because the reflector antenna can simply be rotated at a constant speed to recurrently scan the surrounding area.
In those cases requiring antenna beam agility, reflector antennas are less satisfactory, because the inertia of the antenna results in the need to apply large forces to obtain the necessary accelerations and decelerations. In addition to being costly to operate, the physical stresses on the structure tend to lead to early failure or increased need for maintenance.
As a consequence of these and other disadvantages of reflector-type antennas, attention has been given to the use of array antennas, in which multiple antenna elements or ant elements are arrayed to define a larger radiating aperture, and fed from a common source. In order to achieve beam agility, each antenna element (or groups of antenna elements) is/are associated with controllable phase shifters. In order to improve the range of the communications or of the radar using the phaseshift-controllable array antenna, each antenna element may be associated with a power amplifier, a low-noise receiving amplifier, or both. The combination of the controllable phase shifter for each antenna element, the low-noise receiving amplifier, and the power amplifier, are often combined into a “transmit-receive” (TR) module, together with various switch and control elements, so that modular electronics can be used with the modular antenna elements of the array. U.S. Pat. No. 3,339,086, issued Aug. 16, 1994 in the name of DeLuca et al. describes a phased array antenna in which each elemental antenna element is associated with a transmit/receive (TR) module, but does not describe the physical nature of the structure.
With the increasing range and performance requirements of modern equipments, the power-handling capabilities of the power amplifiers of each of the TR modules of an array antenna have tended to increase. The reliability of electronic equipment tends to be degraded by operation at high temperatures. The increase in power required to be handled by the power amplifiers of TR modules, in turn, leads to the problem of carrying away the additional heat associated with the higher power, so as to keep the electronics at a low, and therefore reliable, temperature. U.S. Pat. No. 5,459,474, issued Oct. 17, 1995 in the name of Mattioli et al. describes an array antenna in which the electronics associated with a column of arrays are in the form of TR modules mounted on a coolant-fluid-carrying cold plate of a slide-in carrier. In the Mattioli et al arrangement, each slide-in carrier has a width no greater than the spacing between adjacent antenna elements. Heat is carried away from each slide-in carrier by coolant flow through a set of hoses, which allow the carriers to be slid toward and away from the antenna array for maintenance. The mounting of a large number of TR modules directly to the cold plate may be disadvantageous, as the entire cold plate must be taken out of service in order to work on or replace a single TR module. The changing out of a defective TR module is complicated by the mechanical fasteners and thermal joining material, or the epoxy bond, often used to provide good physical and thermal mounting of the TR module to the cold plate.
It is desirable to mount small numbers of the TR modules on Line-Replaceable Units (LRUs), which in turn are mounted to the cold plate. The number of TR modules which are mounted on each LRU depends upon a number of factors, among which one major factor is the availability of small-volume, efficient, reasonable-cost power supplies. That is to say, LRUs with but a single TR module may require a power supply which has excess capability for that one TR module, and an array of such LRUs would therefore contain more volume of power supplies than needed. Since volume is a consideration in an array situation, one TR module per LRU might be considered to be undesirable. Similarly, a very large number of TR modules on a single LRU tends to reduce the advantage of a line-replaceable unit, as removal of the LRU takes a large number of TR modules off-line, to the detriment of array operation. With such an arrangement, maintenance on a single TR module can be effected by simply replacing the LRU requiring repair or maintenance with a replacement unit, whereupon the maintenance can be performed off-line while the electronic system or radar continues in operation. Even with the LRU missing, the array can still remain in operation although with degraded capability.
U.S. Pat. No. 6,469,671 describes a system in which a generally planar active array antenna includes a plurality of transmit-receive (TR) modules arrayed in an array direction on a generally planar heat-conducting baseplate of a line-replaceable unit (LRU). Heat is coupled from the TR modules to their associated baseplate. Each baseplate of an LRU has a straight edge parallel to the array direction of the modules. In a preferred embodiment, the modules are located adjacent the straight edge without significant intermediary components. The LRUs are arrayed with their straight edges aligned in a plane. The straight edges are coupled to a generally planar cold plate for extracting heat from the baseplates. Since the heat is extracted in a direction orthogonal to the arraying direction of the modules, all the modules tend to have the same operating temperature. In a particularly advantageous embodiment, the circulators associated with each TR module are mounted on the opposite side of the cold plate relative to the module, to thereby minimize the thermal path length between each module and the cold plate.
Improved or alternative active antenna array structures are desired.